Ultraviolet (UV) lamp systems are commonly used for treating semi-conductor wafers for use in the electronics industry. Certain UV lamp systems have electrodeless light sources and operate by exciting an electrodeless plasma lamp with RF energy, such as microwave energy. In an electrodeless UV lamp system that relies upon excitation with microwave energy, the electrodeless plasma lamp is mounted within a metallic microwave cavity or chamber. One or more RF (radio frequency) or microwave generators, such as magnetrons, are coupled via waveguides with the interior of the microwave chamber. The magnetrons supply microwave energy to initiate and sustain a plasma from a gas mixture enclosed in the plasma lamp. The plasma emits a characteristic spectrum of electromagnetic radiation strongly weighted with spectral lines or photons having UV and infrared wavelengths.
To irradiate a substrate, the UV light is directed from the RF or microwave chamber through a chamber outlet to an external location. The chamber outlet is capable of blocking emission of RF or microwave energy while allowing UV light to be transmitted outside the chamber. A fine-meshed metal screen often covers the chamber outlet of many RF or microwave powered UV lamp systems. The openings in the metal screen transmit the UV light for irradiating a substrate positioned outside the chamber, yet substantially block the emission of RF or microwave energy. In some RF or microwave powered UV lamp systems, a shutter also covers the chamber outlet and is selectively operable to expose the substrate to the UV light.
In existing applications for treating semi-conductor wafers on the order of 300 mm in diameter, UV lamp systems are provided to emit light with the required uniformity, intensity and dosage over the surface area of the wafer. For example, one existing UV lamp system for treating a 300 mm semi-conductor wafer having surface area of 70,685 mm2 uses two 10″ lamp bulbs each powered by two magnetrons to properly surface treat the wafer. These lamp bulbs are configured in parallel to each other. Electrical power in a total amount of 12 kilowatts is provided to the lamp system, or in other words, 600 watts per inch of bulb length. The power density of the system is equal to the total wattage inputted divided by the wafer surface area. In the case of the 300 mm diameter wafer, the power density is therefore 0.1698 w/mm2. One challenge associated with this existing system and others that use multiple magnetrons in a single cavity is the “cross talk” or interference that can exist between the multiple magnetrons, especially at start up. This can damage the magnetrons and lead to shorter life. In addition, the latest semi-conductor wafers are 450 mm in diameter and, therefore, have a surface area of 159,043 mm2, which is much larger in surface area than the 300 mm diameter wafers. Specifically, the surface area is 2.25 times the area of the 300 mm diameter wafer. Therefore, in order to obtain the same power density as needed for the 300 mm diameter wafer the power input requirement for a lamp system used to treat the 450 mm diameter wafer is 27 kilowatts (i.e., 2.25 times 12 kilowatts). However, developing a UV lamp system for treating the 450 mm diameter semi-conductor wafer presents a significant challenge that extends well beyond these basic calculations due to the need for optimum intensity, dosage and uniformity of UV coverage over the entire 450 mm diameter semi-conductor wafer.
There is a need, therefore, for apparatus that achieves the advantages of providing necessary UV radiation intensity and dosage over the entire surface area of a 450 mm diameter semi-conductor wafer while also providing uniform UV radiation across the entire 450 mm diameter semi-conductor wafer and maintaining high productivity.